1. Field of the Invention
This invention relates in general to a submersible centrifugal well pump assemblies, and in particular to an assembly that includes also a downhole secondary pump for injecting scale inhibiting chemicals.
2. Description of the Prior Art
In a conventional well having a centrifugal pump assembly, the well will be cased and will have a string of tubing extending downward to the downhole pump assembly. The pump assembly includes a centrifugal pump mounted above an electrical motor. A seal section mounted between the pump and the motor protects against the entry of well fluid into the motor. Electrical power is supplied by cables extending to the surface. The pump has an intake on its lower end and discharges into the tubing.
In certain fields, scale deposition on the downhole equipment is a serious problem. Mineral scale depositing on the submersible pump assembly can lead to extensive damage. One prior technique used to inhibit the deposition of scale on the equipment is to introduce chemicals into the annulus between the tubing and the casing at the surface. The chemicals will flow downwardly in the annulus into the intake of the pump and back up the tubing. This retards the deposition of scale on the equipment from the intake of the pump inwardly. However, it will not prevent scale deposition below the intake of the pump, and the motor and seal section are located below the intake of the pump.